Alexis Sanchez, Cristian Tello and Lionel Messi all scored within the first 15 minutes, giving the Norwegians a mountain to climb. A goal just before half-time from Jonathan Dos Santos, a double from Jean Marie Dongou, and a late strike from Joan Roman sealed the win for the Catalan side.
It didn't take the Blaugrana long to open up their account, as Alexis put them ahead after just five minutes. Messi picked up the ball in a deep position in midfield and clipped a ball out to the right-hand side for the Chilean, who jinked his way into the box before guiding a left-footed strike home.
Barca doubled their lead just one minute later, with Messi the architect once again. The Argentine found Tello with a lovely threaded pass inside the Valerenga right-back and the 21-year-old coolly stroked the ball home into the bottom right corner.
Never one to be left out of the goals, Messi grabbed the third of the match 13 minutes in. The Barcelona captain for the evening picked up the ball on the edge of the box and drifted past three challenges before reversing a left-footed shot into the bottom corner, giving goalkeeper Lars Hirschfeld no chance.
New Barca coach Gerardo Martino watched from the stands as he witnessed his new side completely dominate the first half, and it could have been much worse for Valerenga in the opening 45 if not for the heroics of Hirschfeld in goal and the woodwork.
The Canadian goalkeeper kept the score relatively low as he pulled of a string of saves from Messi, Tello, and Alexis. Barca were also denied midway through the half when the Argentine clipped a strike towards goal, only to see his attempt crash off the post.
The visitors would not have to wait too long to extend the scoreline, however. Dos Santos made it four just before the break as he latched on to an Alexis pass to the front post before squeezing a shot past Hirschfeld.
It would not get much easier for the Norwegians after half-time as Barca scored two within the first 10 minutes of the second period through substitute, Dongou.
The Cameroonian latched on to a pass through the middle from Alexis and coolly finished. A couple of minutes later he received the ball from the Chilean again as he stabbed a shot home to make it 6-0
Valerenga grew into the match as the second half wore on, however, and almost grabbed a goal to please their home fans. Mohammed Fellah came closest for the Norwegians, but his two strikes from the edge of the box were easily handled by substitute keeper, Oier.
The victory was rounded off for Barcelona five minutes from time when substitute Joan Roman cut inside from the left-hand side and rifled a strike into the top left corner.
Barcelona go on to face Rosenborg in Denmark on Monday as they prepare for the oncoming season and their defence of the Spanish Primera Division.